I’m kind of surprised both you and Rogue seem to think the scientist idea clashes with Rey Nobody. In the grand scheme of things, some clone scientist and his family would be nobody compared to legends such as the Skywalkers and the Palpatines.
The issue is that that would mean her parents were actually of a noble cause and not total drunkards who never amounted to anything. They’re still basically nobody but they’re a good nobody instead of a bad nobody. That’s the difference.
This is one of my top desires for a ST edit. I think it would be cool if Kylo received a vision from the Vader helmet in TFA that clarified his motivation to turn to the dark side. But you also could place Kylo touching Vader’s helmet in TROS at the beginning of that film, and give him a vision there where Vader speaks to him and shows him the way to the Wayfinder.
Right before Palpatine’s reveal would be too late to introduce the concept, so while you can use it there (and in fact it would be good to have as a refresher before the reveal), it’s essentially we introduce the concept much sooner when Kylo speaks to Vader’s helmet in TFA. Funnily enough, this would add another one of JJ Abrams’s beloved mystery boxes but this time it would actually have a fulfilling answer planned out.
The helmet doesn’t appear in TLJ, but you could reutilize footage from TFA or TRoS to add a scene with it. The scene in TFA has Kylo wearing his helmet meaning you could dub him to say just about anything, but it would need to occur before his meeting with Snoke since he destroys his helmet after that. The scene in TRoS just has him touching the helmet with his mask off, not saying a word, so probably not worth trying to reuse.